This invention relates generally to integrated circuit radio frequency transponders, and more particularly, to an integrated circuit radio frequency transponder requiring only one dedicated input pin for signal connection to an externally connected resonant frequency tuned circuit.
Radio frequency transponders may be used in managing inventory, automatic identification of cars on toll roads, building entry, security systems, keyless electronic access and entry devices, and the like. A transponder generally comprises a radio frequency receiver and a radio frequency transmitter and communicates with another related transponder by either first receiving a coded signal and then responding back with a coded transmitted signal, or transmitting a coded signal first then waiting for the correct response to be returned from the related transponder. Any combination of coded signal xe2x80x9chandshakesxe2x80x9d may be utilized by two transponders trying to identify a xe2x80x9cfriendxe2x80x9d or xe2x80x9cfoe.xe2x80x9d Once a friendly coded signal is identified and verified a desired action may be taken, i.e., unlocking a car door, opening a garage door, or building access or egress.
An example of a transponder system is the KEELOQ(copyright) (a registered trademark of Microchip Technology Inc.) Code Hopping Encoder and Transponder, part number HCS412 by Microchip Technology Inc., more fully described in Specification DS41099A (1999), available at http://www.microchip.com, and incorporated by reference herein.
Typically, the transponder amplitude modulates a CW RF carrier of an RF generator with a data word bitstream in accordance with the binary values of that data word bitstream. The data word bitstream is a series of on/off pulses which represent, for example, a serial data word synchronization header, a tag number, etc. Parity bits or a checksum value may also be incorporated into the data word bitstream. These series of on/off pulses are received by the related transponder.
Heretofore, a parallel resonant tuned circuit required connection to two pins of an integrated circuit transponder system. In an integrated circuit package having, for example, multiple functions and/or a plurality of transponder circuits, input-output pin utilization is critical. Requiring two dedicated pins for each parallel resonant circuit associated with a transponder takes away the possibility of using the limited number of pins on the integrated circuit package for other needed or desired functions.
Therefore, what is needed is more effective and better utilization of input-output pins on an integrated circuit package for connecting a parallel resonant circuit to the transponder circuit of the integrated circuit.
The invention overcomes the above-identified problems as well as other shortcomings and deficiencies of existing technologies by providing in an integrated circuit package a transponder requiring only a single dedicated input-output pin (of the integrated circuit package) for connection (external to the package) to a resonant frequency tuned circuit. Another package pin which may be used for common power or ground connections may supply the second connection to the resonant frequency tuned circuit. The transponder embodiment of the present invention may be used in security and access devices for unlocking and opening automobile doors, home and office doors, garage doors, security gates and the like. The present invention enables hands-free operation of locks, doors and the like. Since the transponder is able to receive a low power radio frequency signal, verification and activation of the lock or door may occur from a distance and without having to remove the transponder system from ones pocket, purse, or briefcase.
It is contemplated herein and within the scope of the present invention that an integrated circuit package comprises a plurality of transponder circuits connected to a plurality of associated resonant frequency tuned circuits, each of the plurality of associated resonant frequency tuned circuits requiring a first connection to only a single dedicated input-output pin, and a second connection to a common pin.
It is also contemplated herein and within the scope of the present invention that the dedicated resonant frequency tuned circuit input-output pin(s) may also be used for a secondary function (i.e., dual purpose).
In accordance with an embodiment of the present invention, an integrated circuit package having a transponder circuit therein, has an input-output pin connected to an input of a high gain amplifier biased with current sources also connected to the input of the high gain amplifier. A direct current (DC) bias level measurement and control circuit may be connected to and be in control of these current sources. An input to the DC bias level measurement and control circuit may be a signal received at the input-output pin connected to the input of the high gain amplifier. From the amplitude of the measured input signal, the DC bias level measurement and control circuit may change the DC bias level of the high gain amplifier, thus controlling the gain thereof.
A parallel resonant circuit comprising an inductor connected in parallel with a capacitor forms a pickup sensor or antenna for an externally generated electromagnetic or radio frequency signal. One end of the parallel resonant circuit is connected to a common power or ground pin of the integrated circuit package and the other end of the parallel resonant circuit is connected to one end of a DC blocking capacitor. The other end of the DC blocking capacitor is connected to the input-output pin of the integrated circuit package which is also connected to the input of the high gain amplifier. The reactance of the DC blocking capacitor is preferably substantially less than the input impedance of the high gain amplifier (for example but not limitation: one tenth the impedance) and preferably may also be substantially less than the impedance of the parallel circuit at resonance (for example but not limitation: one tenth the impedance). The DC blocking capacitor thus allows an alternating current (AC) signal coupled to the parallel resonant circuit to pass to the input of the high gain amplifier without the parallel resonant circuit (DC low resistance) affecting the DC bias value from the current sources which are also connected to the input of the amplifier. Alternatively, a DC blocking capacitor may be connected in series with the inductor instead of between the parallel resonant circuit and the input-output pin of the integrated circuit package, and the parallel resonant circuit may then be connected directly to the input-output pin.
An internally generated signal for transmission may be applied to the same pin as used as an input to the transponder amplifier or a separate pin may be utilized to transmit the signal from the integrated circuit. Typical receive or input signal frequencies may be from about 100 kHz to about 14 MHz, and a transmitted output frequency may be from about 100 kHz to well into the ultra high frequency (UHF) range.
In another embodiment of the present invention, an integrated circuit package has a plurality of transponder circuits and a corresponding plurality of input-output pins, each transponder amplifier having an input connected to a one of the corresponding plurality of input-output pins. A plurality of parallel resonant circuits are adapted for connection to the corresponding plurality of input-output pins through DC blocking capacitors and to a common power or ground pin, or the DC blocking capacitors may be connected in series with the inductors, as disclosed above. The plurality of transponder amplifiers and plurality of parallel resonant circuits may be utilized with one signal frequency in a diversity receiving or voting system, or each one of the plurality of parallel resonant circuits may be tuned to a different frequency and the integrated circuit used as multiple simultaneous transponders. Internally generated transmit signals may be applied to the same pin and tuned circuit or may be applied to other pins of the integrated circuit package.
A feature of the present invention is using only one dedicated input-output pin on an integrated circuit package for each transponder function in an integrated circuit.
Another feature is a plurality of transponders in an integrated circuit having a minimum number of input-output pins.
Still another feature is a space diversity or voting system having a plurality of transponders.
An advantage of the present invention is a reduction of the number of input-output pins required for operation of a bi-directional transponder in an integrated circuit.
Another advantage is the operation of the transponder over a desired distance without having to remove the transponder system from a pocket, purse, briefcase and the like.
Features and advantages of the invention will be apparent from the following description of presently preferred embodiments, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.